There were many, many events and issues between 1820 and 1861 that caused the Civil War to come about. Let us look at some of the most important ones:

Nullification controversy. South Carolina threatened to secede over issues relating to tariffs.

Mexican-American War. There was conflict over whether this war was mainly for the purpose of gaining more slave territory.

Fugitive Slave Act. This was part of the Compromise of 1850 that was, in turn, made necessary by the Mexican-American War. This law made many Northerners upset because it forced them to help return escaped slaves to slavery.

Kansas-Nebraska Act. This law reopened the issue of slavery in territories where it was already supposed to have been settled by the Missouri Compromise. It led to the conflicts in “Bleeding Kansas.”

The Dred Scott decision. This decision precluded any further compromises by declaring that Congress could not legislate on the topic of slavery in the territories.

John Brown’s raid. His attempt to start a slave rebellion and reactions to it in the North made the South very unhappy.

The election of Abraham Lincoln. This was the cause of secession since the South felt Lincoln would rule in ways that would only help the North.

Of course, underlying all of these specific issues were the issues of slavery and of states’ rights. All of this helped to bring the Civil War about.